Dalhousie University Department of Physics and Atmospheric Science

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Dalhousie UniversityDepartment of Physics and
Atmospheric Science
Research in Theoretical, Experimental, and
Applied Physics

• Materials Science
• Biophysics
• Condensed Matter Physics
• Atmospheric Science

http//www.physics.dal.ca/files/Physics_and_Atmosp
heric_Science_Faculty.ppt
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Ozone and Aerosols in the Lower Atmosphere

Randall Martin Aaron Van Donkelaar
Kelly Chance Chris Sioris
Arlene Fiore
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GLOBAL RADIATIVE FORCING OF CLIMATE, 1750-present
IPCC 2001
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ORIGIN OF ATMOSPHERIC AEROSOLS
Aerosol dispersed condensed matter suspended in
a gas Size range 0.001 mm (molecular cluster) to
100 mm (small raindrop)
Soil dust Sea salt
Environmental importance health (respiration),
visibility, radiative balance, cloud formation,
heterogeneous reactions, delivery of nutrients
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COMPOSITION OF PM2.5 (NARSTO PM ASSESSMENT)
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Scattering of Radiation
Size Parameter x 2pr/l
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Mie Theory
Extinction Scattering Absorption Extinction
Efficiency (Qext) ratio of the extinction cross
section to the geometric cross-section (pr2)
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MODerate-resolution Imaging Spectroradiometer
(MODIS)
Seven MODIS bands are available for aerosol
properties 0.47, 0.55, 0.65, 0.86, 1.24,
1.64, and 2.13 µm OCEAN reflectance contrast
between cloud-free atmosphere and dark
ocean aerosol optical thickness for all 7
bands LAND reflectance of dark vegetation
and semi-arid regions deduced using 2.13 µm
where aerosols are nearly transparent reflectance
contrast between atmosphere and dense dark
vegetation surface aerosol optical thickness
(0.47 and 0.66 µm)
Optical Thickness
IIoe-?
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What do we actually see?
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Aerosols Visible over Dark Surface
Mar 3, 2003
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Example Cloud and Aerosol Optical Thickness
Aerosol Optical Thickness (550 nm)
Cloud Optical Thickness
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TROPOSPHERIC OZONE IS A KEY SPECIES IN CLIMATE
AND AIR QUALITY

• Major greenhouse gas
• Primary constituent of smog
• Largely controls atmospheric oxidation

Mesosphere
Stratosphere
Ozone layer
Troposphere
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THE ATMOSPHERE IS AN OXIDIZING MEDIUM
Oxidation
Oxidized gas/ aerosol
Reduced gas
Uptake
EARTH SURFACE
Emission
Reduction
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Simplified Tropospheric Ozone (O3) Chemistry
hv
OH
HNO3
NO
NO2
NOx
O3
HO2
OH
H2O2
HOx
hv, H2O
CO, VOCs
CO, VOCs, NOx
VOCs OH ? HCHO HCHO h? ? 2HO2 CO HCHO
OH ? HO2 CO H2O
Role of Formaldehyde (HCHO)
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THE NITROGEN CYCLE MAJOR PROCESSES
combustion lightning
ATMOSPHERE
N2
NO
oxidation
HNO3
denitri- fication
biofixation
deposition
orgN
decay
NH3/NH4
NO3-
BIOSPHERE
assimilation
nitrification
weathering
burial
LITHOSPHERE
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NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE
STRATOSPHERE 0.2
LIGHTNING 6
SOILS 5
FOSSIL FUEL 20
BIOMASS BURNING 5
BIOFUEL 2
AIRCRAFT 0.5
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EULERIAN RESEARCH MODELS SOLVE MASS BALANCE
(alias CONTINUITY) EQUATION IN 3-D ASSEMBLAGE OF
GRIDBOXES
Solve continuity equation for individual gridboxes

• Models can presently afford
• 106 gridboxes
• In global models, this implies a horizontal
  resolution of 100-500 km in horizontal and 1 km
  in vertical

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BOTTOM-UP EMISSION INVENTORIES ARE NOTORIOUSLY
DIFFICULT TO DETERMINE

• Fuel use estimates
• Measurements of emission ratios
• Process studies
• Estimate biological density
• Temperature, water, dependence of biological
  activity
• Extreme events

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Absorbing properties of molecules
Atmospheric trace gas absorptions detected in
satellite spectra
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Retrieval of Trace Gas Column
Nonlinear least-squares fitting
Solar Io
Backscattered intensity IB
Scattering by Earth surface and by atmosphere
A
EARTH SURFACE
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Total NO2 Slant Columns Observed from the
SCIAMACHY Satellite Instrument
May-August 2004
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Perform a Radiative Transfer Calculation to
Account for Viewing Geometry and ScatteringCloud
Screening Remove Scenes with IB,c gt IB,o
IB,c
IB,o
Io
q

• LIDORT Radiative Transfer Model Spurr et al.,
  2002
• FRESCO Clouds Fields Koelemeijer et al., 2002
• GOME Surface Reflectivity Koelemeijer et al.,
  2003

Rc
Ro
Pc
dt
Rs
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Tropospheric NO2 Columns Observed from the
SCIAMACHY Satellite Instrument
May-August 2004
detection limit
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Major Urban Centers Are Concentrated NOx Sources
May-August 2004
detection limit
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Ozone Control Strategies Require Independent
Information on Effectiveness of Reducing NOx or
VOCs
Shown that the HCHO/NO2 Ratio Is as
Indicator That Can be Observed from Space
(ppbv)
NOx-Saturated
NOx-Limited
Sillman and He, 2002
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GOME Observations Show NOx-Sensitive Conditions
Over Most Polluted Regions During AugustMajor
Industrial Areas are Clear Exceptions
White areas indicate clouds or data below the
GOME detection limit
August
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Biomass Burning Emissions are Clearly
NOx-Sensitive, In Contrast with NOx-Saturated
Conditions Over the Industrial Highveld
Also observe plume evolution
August
NOx Lim
NOx Lim
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Seasonal Evolution from NOx-Sensitive to
NOx-Saturated Conditions in Fall
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